Gorgolewski Krzysztof J, Storkey Amos J, Bastin Mark E, Pernet Cyril R
School of Informatics, Nauroinformatics and Computational Neuroscience Doctoral Training Centre, University of Edinburgh Edinburgh, UK.
Front Hum Neurosci. 2012 Aug 25;6:245. doi: 10.3389/fnhum.2012.00245. eCollection 2012.
Single subject fMRI has proved to be a useful tool for mapping functional areas in clinical procedures such as tumor resection. Using fMRI data, clinicians assess the risk, plan and execute such procedures based on thresholded statistical maps. However, because current thresholding methods were developed mainly in the context of cognitive neuroscience group studies, most single subject fMRI maps are thresholded manually to satisfy specific criteria related to single subject analyzes. Here, we propose a new adaptive thresholding method which combines Gamma-Gaussian mixture modeling with topological thresholding to improve cluster delineation. In a series of simulations we show that by adapting to the signal and noise properties, the new method performs well in terms of total number of errors but also in terms of the trade-off between false negative and positive cluster error rates. Similarly, simulations show that adaptive thresholding performs better than fixed thresholding in terms of over and underestimation of the true activation border (i.e., higher spatial accuracy). Finally, through simulations and a motor test-retest study on 10 volunteer subjects, we show that adaptive thresholding improves reliability, mainly by accounting for the global signal variance. This in turn increases the likelihood that the true activation pattern can be determined offering an automatic yet flexible way to threshold single subject fMRI maps.
单受试者功能磁共振成像已被证明是一种在诸如肿瘤切除等临床手术中绘制功能区域的有用工具。利用功能磁共振成像数据，临床医生基于阈值化统计图谱评估风险、规划并执行此类手术。然而，由于当前的阈值化方法主要是在认知神经科学群体研究的背景下开发的，大多数单受试者功能磁共振成像图谱需手动设置阈值以满足与单受试者分析相关的特定标准。在此，我们提出一种新的自适应阈值化方法，该方法将伽马-高斯混合建模与拓扑阈值化相结合以改善聚类描绘。在一系列模拟中，我们表明，通过适应信号和噪声特性，新方法在错误总数方面表现良好，而且在假阴性和阳性聚类错误率之间的权衡方面也表现出色。同样，模拟表明，在真实激活边界的高估和低估方面（即更高的空间准确性），自适应阈值化比固定阈值化表现更好。最后，通过对10名志愿者受试者进行模拟和运动重测研究，我们表明自适应阈值化提高了可靠性，主要是通过考虑全局信号方差。这反过来又增加了确定真实激活模式的可能性，为单受试者功能磁共振成像图谱提供了一种自动且灵活的阈值化方法。
